The invention relates generally to implantable medical devices or systems, and more particularly to a neural stimulator having percutaneous connectivity between implanted and external (non-implanted) components of the device or system.
A neural stimulator is an electrical stimulator that selectively applies electrical stimulation to a target stimulation site, usually a nerve, muscle or other body tissue. Neurostimulation systems have been used to provide electrical stimuli to the heart, spinal cord system, peripheral nerves, lungs, inner ear, brain, and many other body organs and tissue.
A problem that has long plagued the use of implantable medical devices is establishing reliable connectivity between implanted and external (non-implanted) portions or components of the system. Most, if not all, implantable medical devices and systems include one or more external components used with one or more implanted components. The external component(s) may be simple or complex. For example, the external component may be as simple as a permanent magnet that is placed over a magnetic reed switch located inside of the implanted device. When the magnet is placed over the magnetic reed switch, the state of the magnetic reed switch changes, which in turn may change the operating mode or state of the implanted device. Alternatively, the external component may be as complex as a programming/monitoring device that allows a user to program the implanted device to operate in accordance with a very sophisticated operating procedure.
Similarly, the implantable component(s) may be simple or complex. For example, the implanted component may be as simple as a wire or lead having an electrode at a distal end. The distal end is placed near tissue that is to be stimulated (referred to herein as “target tissue”), while the proximal end is placed near the surface of the skin, but still under the skin, where it can be coupled more efficiently to an external source of stimulation energy. Alternatively, the implanted component(s) may be as complex as a fully implantable medical device that selectively generates and applies electrical stimulation to target tissue through at least one of a large number of electrodes as a function of sensed conditions or events, and that further regularly transmits status signals to an external device to provide a status report of its operating condition.
Regardless of the complexity or simplicity of the implanted or external components of the system, there is a critical need for the implanted and external components to reliably communicate with each other at certain times during the operation of the system.
Early in the development of implantable medical devices, connectivity between the implanted and external components was achieved by simply passing a wire through the skin, with a proximal end of the wire being connected to the external device and a distal end being connected to the implanted device. (Typically, rather than having a wire or lead dangling from an incision in the skin, a connector of some type was used near the skin surface to allow easy detachable connectivity with the connector at a point near the skin surface so that only a short length of wire extended from the skin. However, the wire on the back side of the connector still passed through the skin.) Such wire provided good connectivity, but created other problems, most notably soreness and infection. As a result, a wire passing directly through the skin could never be left in place for very long without constant attention being given to keeping the hole or stoma through which the wire passed clean and disinfected.
For example, a cochlear implant system is described in U.S. Pat. No. 4,400,590 which uses wire(s) passing through the skin. However, in use, such system left an opening in the patient's skin through which infection could easily enter. Thus, because infection was a continual risk, use of a wire-through-the-skin to provide electrical connectivity between external and implanted components of a cochlear implant system of the type described in U.S. Pat. No. 4,400,590 was effectively abandoned over 25 years ago.
In order to ameliorate the disadvantages associated with a wire passing directly through the skin, other types of signal coupling links have been employed that do not require a direct signal connection through an opening made in the skin. Such links pass a signal through the skin without wires, i.e., a wireless communication. Typically, such wireless signal transfer links have included inductive coupling or radio-frequency (RF) coupling, but other types of wireless communication links are also known, e.g., optical coupling, magnetic coupling, infrared coupling, and the like.
The problem with wireless communication links, however, is that they require additional electronic circuitry on both the transmitting side and receiving side of the link. Such additional communication circuitry disadvantageously adds to the complexity, cost, size, power consumption, and efficiency of the system. Moreover, such additional communication circuitry reduces the overall reliability of the system because it inherently includes additional critical components which could fail, and in the event of such failure, shut down the system, or worse, cause the system to operate in an unsafe manner. Hence, there remains a critical need to develop smaller, simpler, more reliable, and more efficient communication links for use between the implanted and external components of an implantable medical device system.
To address this need, some have recently proposed going back to the wire-through-the-skin approach, while taking precautions to minimize the undesirable effects (soreness and infection) that normally occur when any foreign object is inserted in, or passes through, the skin. See, e.g., patent publication US 2008/0243216, published Oct. 2, 2008, entitled “System and Method For Percutaneous Delivery of Electrical Stimulation To a Target Body Tissue”, hereafter the '216 Publication, which publication is incorporated herein by reference in its entirety.
In accordance with the teachings of the '216 publication, an conductive stub is embedded in the skin so as to provide an electrical pathway for electrically connecting an external component and an implanted component. At least one embodiment suggests that this stub be electrically insulated except at its distal and proximal tips. The insulation around the stub is made from a biocompatible material that has a fibrous or porous layer on its outer surface. Thus, when the stub is inserted through an incision made in the skin, tissue ingrowth into the fibrous or porous layer will occur over time thereby promoting anchorage and sealing of the epidermas around the stub. That is, a fibrin clot forms around the outer surface of the insulation that, in theory, acts as a barrier to infection, and over time becomes new skin integral with the stub. Such tissue ingrowth further serves to hold the stub in place. See, paragraphs [0089] and [0090] of the '216 Publication.
While the “stub” approach described in the '216 publication may provide a viable alternative for making a direct electrical connection through the skin when only a small number of percutaneous direct electrical connections are needed, e.g., one or two, many implantable systems used today require many more percutaneous connections than just one or two. In such situations, the “stub” approach is unsightly and unsatisfactory.
Thus, it is seen that there remains a critical need for improved connectivity between external and implanted components of a neurostimulation system. More particularly, there is a need for a percutaneous communication link that provides direct electrical connection through the skin while avoiding the problems of infection and soreness that have plagued previous through-the-skin approaches, and that also allows a sufficiently large number of independent, direct electrical connections through the skin in order to support the operation of the most sophisticated and complex medical device systems.